Graphene / nanocellulose composite broadband terahertz wave absorber based on microdroplet spraying and preparation method and application of graphene / nanocellulose composite broadband terahertz wave absorber

Abstract

The invention discloses a graphene / nanocellulose composite broadband terahertz wave absorber based on microdroplet jetting and a preparation method and application thereof, and relates to the technical field of terahertz wave absorption. The method comprises the following steps: preparing a graphene / nanocellulose composite film; a nano cellulose film is prepared; graphene ink is obtained; and printing graphene ink onto the nano-cellulose film according to a preset pattern by adopting a micro-droplet jetting method to obtain the nano-cellulose film printed with the graphene metamaterial. The terahertz wave absorber can be formed by bonding the metal plate, the graphene / nanocellulose composite film and the nanocellulose film printed with the graphene metamaterial through a trace amount of binder. The wave absorber is short in production period, simple in preparation process, low in cost and free of environmental pollution.

Description

Technical Field

[0001] The present invention relates to the field of terahertz wave absorbing technology, and in particular to a graphene / nanocellulose composite broadband terahertz wave absorber based on droplet injection, and a preparation method and application thereof. Background Art

[0002] Terahertz waves possess strong penetrability, low energy, and high resolution, enabling terahertz detection to overcome many conventional detection barriers and possessing significant strategic value in the military. With the advancement of terahertz detection technology, the development of terahertz absorbers capable of countering terahertz detection has become increasingly critical. Metamaterial absorbers absorb electromagnetic waves in specific frequency bands through electromagnetic resonance mechanisms. Their compact structure and thinness have made them a research hotspot for terahertz absorption. Traditional metamaterial absorbers consist of a metamaterial layer, a dielectric layer, and a metal layer. The metamaterial layer is typically made of metal, which is dense and susceptible to corrosion after prolonged use. Graphene, due to its light weight, excellent optoelectronic properties, and stable physicochemical properties, has become an excellent candidate for metamaterial absorbers.

[0003] Achieving broadband absorption is key to improving equipment stealth capabilities and is a core performance characteristic of metamaterial absorbers. While graphene metamaterial-based terahertz absorbers have been fabricated through chemical vapor deposition and photolithography, capable of absorbing single- or multi-frequency terahertz waves, the fabrication of terahertz absorbers with broadband absorption performance remains challenging. Researchers have attempted to design broadband terahertz metamaterial absorbers by arranging multiple metamaterial units in a plane or stacking metamaterials vertically. However, due to the limitations of chemical vapor deposition and photolithography, the development of broadband terahertz metamaterial absorbers has largely remained at the simulation and design stage, hindering their practical fabrication. Existing technologies have fabricated a graphene-water-based terahertz metamaterial absorber using techniques such as DC magnetron sputtering, atomic layer deposition, reactive ion etching, microinjection, photolithography, and oxygen plasma etching, achieving ultra-broadband terahertz wave absorption from 3.8 to 9 THz. However, the graphene metamaterial is fabricated using chemical vapor deposition and photolithography, a time-consuming and complex process. Furthermore, magnetron sputtering of aluminum layers and atomic layer deposition of aluminum oxide pose high costs, limiting their potential for engineering applications. Existing fabrication methods are not yet capable of cost-effective and flexible fabrication of broadband terahertz absorbers. New fabrication methods are needed to achieve efficient fabrication of broadband terahertz absorbers. Summary of the Invention

[0004] In response to the shortcomings of the aforementioned background technology, the present invention primarily overcomes the difficulties in preparing broadband terahertz absorbers. It provides a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection, as well as its preparation method and application. This method deposits nanocellulose-dispersed graphene ink onto a nanocellulose substrate via droplet injection. The abundant hydrogen bonds within the nanocellulose enhance the adhesion of the graphene to the substrate, resulting in improved operational stability for the absorber.

[0005] The first object of the present invention is to provide a method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection, comprising the following steps: The graphene powder and nanocellulose powder are uniformly dispersed in an aqueous solvent to obtain a graphene / nanocellulose dispersion; the graphene / nanocellulose dispersion is deposited onto a supporting substrate by a casting method, and dried to obtain a graphene / nanocellulose composite film; The nanocellulose dispersion is deposited onto a supporting substrate by a casting method, and dried to obtain a nanocellulose film; uniformly dispersing graphene powder in nanocellulose dispersion to obtain graphene ink; Printing graphene ink onto the nanocellulose film using a droplet jetting method according to a preset pattern to obtain a nanocellulose film printed with graphene metamaterials; The metal plate, the graphene / nanocellulose composite film and the nanocellulose film printed with the graphene metamaterial are stacked and bonded in sequence to obtain a graphene / nanocellulose composite broadband terahertz absorber based on droplet jetting.

[0006] Preferably, during lamination and bonding, the graphene metamaterial in the nanocellulose film printed with the graphene metamaterial is arranged away from one side of the graphene / nanocellulose composite film.

[0007] Preferably, when preparing the graphene / nanocellulose dispersion, the mass ratio of the graphene powder to the nanocellulose powder is 1:3 to 4:5.

[0008] Preferably, the mass concentration of the nanocellulose dispersion is 0.5-1.5%.

[0009] Preferably, when preparing graphene ink, the mass ratio of graphene powder to nanocellulose in the nanocellulose dispersion is 6:1 to 7:1.

[0010] Preferably, when the graphene ink is printed onto the nanocellulose film using a droplet jetting method, the printing rate is set to 0.6 to 1 mm / s.

[0011] Preferably, the preset pattern includes a plurality of periodically arranged structural units; each structural unit is composed of a square ring and two mutually intersecting and perpendicular "I"-shaped structures nested therein; Each "I"-shaped structure includes a vertical rod and horizontal rods arranged at both ends of the vertical rod, and the two horizontal rods are arranged relatively parallel; Two mutually intersecting and perpendicular "I"-shaped structures include two "I"-shaped structures in which vertical rods are mutually intersecting and perpendicularly arranged; The two parallel horizontal bars in each "I" structure are of equal length; In each graphene metamaterial unit, a gap is left between the ends of the two cross bars in one "I" structure and the ends of the two cross bars in another "I" structure.

[0012] Preferably, the metal plate is copper, aluminum or silver; the thickness of the metal plate is 10-30 µm; the thickness of the graphene / nanocellulose composite film is 10-40 µm; and the thickness of the nanocellulose film printed with graphene metamaterial is 10-40 µm.

[0013] The second object of the present invention is to provide a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection.

[0014] The third object of the present invention is to provide a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection for use in terahertz wave absorption.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a graphene / nanocellulose composite broadband terahertz absorber based on droplet jetting, as well as its preparation method and application. The invention utilizes uniform droplet jetting technology to print a graphene metamaterial layer, overcoming the limitations of traditional photolithography. This technology allows for the precise and rapid construction of arbitrarily complex micropatterns through digital printing, achieving high-precision molding of graphene metamaterials. Furthermore, a graphene ink dispersed in nanocellulose is deposited onto a nanocellulose substrate via droplet jetting. The abundant hydrogen bonds within the nanocellulose enhance the adhesion of the graphene to the substrate, resulting in excellent operational stability for the absorber. Furthermore, the prepared graphene / nanocellulose and nanocellulose dispersions exhibit uniform dispersion, suitable viscosity, and surface tension, enabling the fabrication of thin films using a casting method. This film achieves uniform and easily controllable thickness, high production efficiency, and further optimizes the production process. Finally, a metal plate, graphene / nanocellulose composite film, and nanocellulose film printed with the graphene metamaterial are bonded together using a trace amount of adhesive to form the terahertz absorber. This absorber features a short production cycle, a simple preparation process, low cost, and no environmental impact. The present invention provides a cost-effective manufacturing method for the industrial preparation of broadband terahertz absorbers.

[0016] The principle of the absorber provided by the present invention to achieve wave absorbing performance is as follows: the top layer of graphene metamaterial excites local resonance through artificial microstructures, forming a strong electric field at a specific frequency point to enhance electromagnetic loss. The nanocellulose dielectric layer is the carrier of the metamaterial, which is used to separate the metamaterial layer and the composite material layer to prevent the electromagnetic loss effects of the metamaterial and the composite material from being affected by each other. The graphene / nanocellulose composite material layer provides a broadband dielectric loss substrate through the strong polarization relaxation effect of its heterogeneous interface, bridges the discrete resonance peaks, and expands the absorption bandwidth. The metal layer serves as the bottom layer, and through total reflection, the residual wave is reflected back to penetrate the middle layer, driving the electromagnetic wave to lose its energy through multiple reflections. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart for preparing composite structure broadband graphene terahertz absorbers.

[0018] Figure 2 Schematic diagram of the device for uniform droplet jet printing of graphene metamaterials.

[0019] In the figure, 1-computer, 2-CCD camera, 3-pulse signal generator, 4-piezoelectric nozzle, 5-graphene droplet, 6-infusion tube, 7-liquid reservoir, 8-LED light, 9-3D motion platform, 10-printing platform, 11-3D motion platform controller.

[0020] Figure 3 This is an optical microscope image of the graphene metamaterial THz absorber.

[0021] Figure 4 This is a physical picture of the THz absorber sample.

[0022] Figure 5 This is the terahertz absorption spectrum obtained by testing the terahertz absorber. The terahertz absorber can achieve 90% absorption in the 0.4~3 THz frequency band. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0024] The purpose of the present invention is to provide a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection, and its preparation method and application, so as to overcome the difficulty in preparing broadband terahertz absorbers.

[0025] In order to achieve the above objectives, the first aspect of the present invention provides a method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection, comprising the following steps: The graphene powder and nanocellulose powder are uniformly dispersed in an aqueous solvent to obtain a graphene / nanocellulose dispersion; the graphene / nanocellulose dispersion is deposited onto a supporting substrate by a casting method, and dried to obtain a graphene / nanocellulose composite film; The nanocellulose dispersion is deposited onto a supporting substrate by a casting method, and dried to obtain a nanocellulose film; uniformly dispersing graphene powder in nanocellulose dispersion to obtain graphene ink; Printing graphene ink onto the nanocellulose film using a droplet jetting method according to a preset pattern to obtain a nanocellulose film printed with graphene metamaterials; The metal plate, the graphene / nanocellulose composite film and the nanocellulose film printed with the graphene metamaterial are stacked and bonded in sequence to obtain a graphene / nanocellulose composite broadband terahertz absorber based on droplet jetting.

[0026] This invention uses uniform microdroplet jetting technology to print graphene metamaterial layers, overcoming the limitations of traditional photolithography. This digital printing method allows for the precise and rapid construction of micropatterns of arbitrarily complex shapes, achieving high-precision molding of graphene metamaterials. Furthermore, by depositing nanocellulose-dispersed graphene ink onto a nanocellulose substrate through microdroplet jetting, the abundant hydrogen bonds within the nanocellulose enhance adhesion between the graphene and the substrate, resulting in improved operational stability for the absorber.

[0027] The absorber's absorbing performance is achieved by the following principle: an incident electromagnetic wave first triggers the localized resonance of the top-layer artificial microstructured graphene metamaterial, focusing the electric field energy at a specific frequency point to achieve efficient narrowband capture. The intermediate isolation layer composed of nanocellulose effectively decouples the top-layer resonance from the broadband dissipation mechanism of the underlying composite material. The graphene / nanocellulose heterointerface stimulates strong polarization relaxation, resulting in continuous broadband loss and expanding the absorption band. The bottom-layer metal reflective interface directs the residual electromagnetic energy back, causing it to be repeatedly reflected in the multilayer structure until it is fully attenuated.

[0028] During lamination and bonding, the graphene metamaterial in the nanocellulose film printed with the graphene metamaterial is placed away from the graphene / nanocellulose composite film. During the lamination and bonding process, a trace amount of adhesive is used for bonding.

[0029] When preparing the graphene / nanocellulose dispersion, the mass ratio of the graphene powder to the nanocellulose powder is 0.3-0.8:1.

[0030] The mass concentration of the nanocellulose dispersion is 0.5-1.5%.

[0031] When preparing graphene ink, the mass ratio of graphene powder to nanocellulose in the nanocellulose dispersion is 6~7:1.

[0032] When graphene ink is printed onto the nanocellulose film using a droplet jetting method, the printing rate is set to 0.6 ~ 1 mm / s.

[0033] The metal plate is copper, aluminum or silver; The thickness of the metal plate is 10-30 μm; the thickness of the graphene / nanocellulose composite film is 10-40 μm; and the thickness of the nanocellulose film printed with graphene metamaterial is 10-40 μm.

[0034] See also Figure 3 As shown, the preset pattern includes multiple structural units arranged periodically; each structural unit is composed of a square ring and two mutually intersecting and perpendicular "I" structures nested inside it; Each "I"-shaped structure includes a vertical rod and horizontal rods arranged at both ends of the vertical rod, and the two horizontal rods are arranged relatively parallel; Two mutually intersecting and perpendicular "I"-shaped structures include two "I"-shaped structures in which vertical rods are mutually intersecting and perpendicularly arranged; The two parallel horizontal bars in each "I" structure are of equal length; In each graphene metamaterial unit, a gap is left between the ends of the two cross bars in one "I" structure and the ends of the two cross bars in another "I" structure.

[0035] For example, see Figure 1 As shown, a method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection comprises: Step 1: Graphene powder and nanocellulose powder are mixed in a mass ratio of approximately 0.3 to 0.8 and added to deionized water. A graphene / nanocellulose dispersion is prepared using simultaneous mechanical stirring and waterbath sonication at a stirring speed of 1600 rpm, an ultrasonic power of 80 W, and a treatment time of approximately 1.5 to 2 hours. A support substrate is selected from materials such as plexiglass, PET, or a glass slide. After ultrasonic cleaning and drying with a balloon, the graphene / nanocellulose dispersion is deposited onto the support substrate using a casting method and dried at room temperature for approximately 48 hours to form a graphene / nanocellulose composite film.

[0036] Step 2: Add nanocellulose powder to deionized water to prepare a nanocellulose dispersion with a mass fraction of approximately 1%. The nanocellulose dispersion is mechanically stirred for 1 to 1.5 hours at 1600 rpm and vacuum defoamed for 1 to 3 minutes to obtain a uniform, bubble-free nanocellulose dispersion. After ultrasonically cleaning the support substrate and drying it with a balloon, the nanocellulose dispersion is deposited onto the support substrate using a casting method and dried at room temperature for approximately 48 hours to form a nanocellulose film.

[0037] Step 3: Graphene sheets and nanocellulose powder were weighed in a mass ratio of approximately 6 to 7. The nanocellulose powder was first added to deionized water and mechanically stirred at 1600 rpm for approximately 10 minutes to prepare a nanocellulose dispersion. The graphene powder was then added to the nanocellulose dispersion and probe ultrasound was used to evenly disperse the graphene sheets at a power of 120 to 180 W for 1.5 to 3 hours to obtain a stably dispersed graphene ink suitable for droplet jetting.

[0038] Step 4, see Figure 2 As shown, the device for uniformly printing graphene metamaterials by microdroplet jetting comprises: Computer 1, CCD camera 2, pulse signal generator 3, piezoelectric nozzle 4, graphene droplet 5, infusion tube 6, liquid reservoir 7, LED light 8, 3D motion platform 9, printing platform 10, 3D motion platform controller 11. Computer 1 controls the pulse signal generator 3 to drive the piezoelectric nozzle 4 to spray graphene droplet 5, and controls the 3D motion platform controller 11 to precisely position the 3D motion platform 9 and printing platform 10. Ink in the liquid reservoir 7 is supplied to the nozzle 4 via the infusion tube 6. Simultaneously, the CCD camera 2 monitors the spraying process under the illumination of the LED light 8 and feeds the image back to the computer 1.

[0039] Ultrasonic cleaning of the piezoelectric nozzle 4, infusion tube 6, and liquid reservoir 7 was performed at a power of 60-80 W for 20-30 minutes. After the ultrasonic cleaning was completed, the piezoelectric nozzle 4, infusion tube 6, and liquid reservoir 7 were connected. The pulse width and frequency of the pulse signal output by the pulse signal generator 3 were adjusted. When the pulse signal parameters were adjusted to a pulse width of 15-20 µs, a frequency of 10-15 Hz, and a printing rate of 0.6-1 mm / s, the graphene droplets 5 were stably ejected and printed in a uniform, straight line.

[0040] Step 5: Create and execute a printing program on a computer based on the designed graphene metamaterial pattern. By collaboratively controlling the movement of the 3D motion platform and the ejection of graphene droplets from the piezoelectric nozzle, the graphene droplets are deposited point by point on the surface of the nanocellulose film, forming a pattern consisting of a square ring with two intersecting, perpendicular "I"-shaped structures nested within it. This printing program is repeated multiple times, performing multi-layer graphene printing to obtain the graphene metamaterial pattern.

[0041] Step 6: Select a highly conductive metal such as copper, aluminum, or silver as the absorber's base plate. After ultrasonically cleaning the metal plate and drying it with a balloon, bond the metal plate, graphene / nanocellulose composite film, and nanocellulose film printed with the graphene metamaterial using a small amount of epoxy resin. This completes the terahertz absorber, with a total thickness of approximately 80-100 µm. The graphene metamaterial layer is positioned away from the graphene / nanocellulose composite film. Specifically, the metal plate, graphene / nanocellulose composite film, and nanocellulose film printed with the graphene metamaterial are bonded together in order, from bottom to top, with the graphene metamaterial layer facing upward.

[0042] A second aspect of the present invention provides a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection.

[0043] A third aspect of the present invention provides an application of a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection in terahertz wave absorption.

[0044] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0045] Example 1 See also Figure 1 As shown, the specific steps of the method for preparing a composite structure broadband graphene terahertz absorber based on droplet injection technology are as follows: Step 1. Graphene powder and nanocellulose powder were mixed in a mass ratio of 1:3 and added to deionized water. A graphene / nanocellulose dispersion was prepared using waterbath ultrasound combined with mechanical stirring at a stirring speed of 1600 r / min and an ultrasonic power of 80 W. After ultrasonic cleaning the support substrate and drying it with a balloon, the graphene / nanocellulose dispersion was cast onto a 3 cm × 3 cm organic glass substrate. The film was dried at room temperature for approximately 48 hours to form a graphene / nanocellulose composite film approximately 20 µm thick.

[0046] Step 2: Add nanocellulose powder into deionized water to prepare a nanocellulose dispersion with a mass fraction of about 1%. Stir the nanocellulose solution for 1.5 h and treat it by vacuum defoaming for 2 min. After ultrasonic cleaning the support substrate and drying it with a balloon, deposit the nanocellulose dispersion onto a 3 cm × 3 cm plexiglass substrate by the casting method and dry it at room temperature for about 48 h to form a nanocellulose film with a thickness of about 40 µm.

[0047] Step 3: Weigh graphene powder and nanocellulose powder according to a mass ratio of about 6:1. First, add the nanocellulose powder into deionized water and mechanically stir it for about 10 min at a stirring rate of 1600 r / min to prepare a nanocellulose dispersion. Then add the graphene powder into the nanocellulose dispersion and use a probe ultrasonic to make the graphene sheets disperse uniformly. The ultrasonic power is 120 w and the time is 3 h to obtain a stably dispersed graphene ink.

[0048] Step 4: Ultrasonically clean the piezoelectric nozzle 4, the infusion tube 6, and the reservoir 7 with a power of 60 w for 30 min. After the ultrasonic cleaning, connect the piezoelectric nozzle 4, the infusion tube 6, and the reservoir 7. Adjust the pulse width and frequency of the pulse signal output by the pulse signal generator 3. When the pulse signal parameters are adjusted to a pulse width of 15 - 20 µs, a frequency of 15 Hz, and a printing rate of 1 mm / s, the graphene microdroplets 5 can achieve stable jetting and uniform linear printing.

[0049] Step 5: Write and execute a printing program on the computer according to the preset pattern of the designed graphene metamaterial. By coordinately controlling the movement of the three-dimensional motion platform and the jetting of the graphene microdroplets from the piezoelectric nozzle, make the graphene deposit point by point on the surface of the nanocellulose film to form the expected pattern. Loop this printing program to repeat it multiple times for multi-layer graphene printing to obtain the graphene metamaterial, as shown in Figures 3 and 4 shown.

[0050] Among them, the period of the metamaterial unit in the preset pattern p , the side length of the square ring pattern l , the vertical bar length of the "I" - shaped pattern d 1 and the horizontal bar length d 2 are specifically p = 1800 μm, l = 1200 μm, d 1 = 800 μm, d 2 = 400 μm.

[0051] Step 6. Select a copper foil with a thickness of 0.02 mm and cut it into thin sheets of 3 cm × 3 cm. After ultrasonically cleaning the copper metal plate and blowing it dry with a balloon, a 20 µm thick copper foil, a 20 µm thick graphene / nanocellulose composite film, and a 40 µm thick nanocellulose film printed with graphene metamaterials are bonded together with a trace amount of epoxy resin to form a formed terahertz absorber with a total thickness of 85 µm.

[0052] Example 2 See also Figure 1 As shown, the specific steps of the method for preparing a composite structure broadband graphene terahertz absorber based on droplet injection technology are as follows: Step 1. Graphene powder and nanocellulose powder were mixed in a mass ratio of 1:2 and added to deionized water. A graphene / nanocellulose dispersion was prepared using waterbath ultrasonication and stirring at a stirring speed of 1600 r / min and an ultrasonic power of 80 W. After ultrasonically cleaning the substrate and drying it with a balloon, the graphene / nanocellulose dispersion was cast onto a 2 cm × 2 cm glass slide and dried at room temperature for approximately 48 hours to form a 20 µm thick graphene / nanocellulose composite film.

[0053] Step 2: Add nanocellulose powder to deionized water to prepare a nanocellulose dispersion with a mass fraction of approximately 1%. Stir the nanocellulose dispersion for 1.5 hours and degas under vacuum for 2 minutes. After ultrasonically cleaning the support substrate and drying it with a balloon, the nanocellulose dispersion was cast onto a 2 cm × 2 cm glass slide and dried at room temperature for approximately 48 hours to form a nanocellulose film approximately 40 µm thick.

[0054] Step 3: Graphene sheets and nanocellulose powder were weighed in a mass ratio of approximately 7:1. The nanocellulose powder was first added to deionized water and mechanically stirred at 1600 rpm for approximately 10 minutes to prepare a nanocellulose dispersion. The graphene powder was then added to the nanocellulose dispersion and probe ultrasound was used to evenly disperse the graphene sheets at a power of 150 W for 2 hours to obtain a stably dispersed graphene ink.

[0055] Step 4: Ultrasonic cleaning of the piezoelectric nozzle 4, infusion tube 6, and reservoir 7 was performed at 60 W for 30 minutes. After ultrasonic cleaning, the piezoelectric nozzle 4, infusion tube 6, and reservoir 7 were connected. When the process parameters were adjusted to a pulse width of 15 to 20 µs, a frequency of 12 Hz, and a print rate of 0.8 mm / s, the graphene droplets 5 were stably ejected and printed in a uniform, straight line.

[0056] Step 5: Create and execute a printing program based on the designed graphene metamaterial on a computer. By collaboratively controlling the movement of the 3D motion platform and the ejection of graphene droplets from the piezoelectric nozzle, graphene is deposited point by point on the surface of the nanocellulose film to form the desired pattern. This printing program is repeated multiple times to print multiple layers of graphene, yielding the graphene metamaterial.

[0057] Step 6: Select aluminum foil with a thickness of 0.02 mm and cut it into thin sheets of 2 cm × 2 cm. Ultrasonic clean the aluminum sheet and blow it dry with a balloon. Then, glue the aluminum foil, graphene / nanocellulose composite film, and nanocellulose film printed with graphene metamaterials with a small amount of epoxy resin to form a terahertz absorber. The total thickness of the absorber is about 85 µm.

[0058] In order to illustrate the performance of the composite structure broadband graphene terahertz absorber based on the droplet ejection technology prepared by the present invention, it is described with reference to the accompanying drawings.

[0059] Figure 5 This is the terahertz absorption spectrum obtained by testing the terahertz absorber provided in Example 1. The terahertz absorber can achieve 90% absorption in the 0.4-3 THz frequency band. Strong absorption of electromagnetic waves is achieved through electromagnetic resonance of the graphene metamaterial layer and polarization relaxation effects at the heterogeneous interface in the graphene / nanocellulose composite layer.

[0060] The present invention describes preferred embodiments and their effects. However, those skilled in the art, once informed of the basic inventive concept, may make additional changes and modifications to these embodiments. Therefore, it is intended that the appended claims be interpreted to include the preferred embodiments as well as all changes and modifications that fall within the scope of the invention.

[0061] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection, characterized in that: The following steps are involved: The graphene powder and nanocellulose powder are uniformly dispersed in an aqueous solvent to obtain a graphene / nanocellulose dispersion; the graphene / nanocellulose dispersion is deposited onto a supporting substrate by a casting method, and dried to obtain a graphene / nanocellulose composite film; The nanocellulose dispersion is deposited onto a supporting substrate by a casting method, and dried to obtain a nanocellulose film; uniformly dispersing graphene powder in nanocellulose dispersion to obtain graphene ink; Printing graphene ink onto the nanocellulose film using a droplet jetting method according to a preset pattern to obtain a nanocellulose film printed with graphene metamaterials; The metal plate, the graphene / nanocellulose composite film and the nanocellulose film printed with the graphene metamaterial are stacked and bonded in sequence to obtain a graphene / nanocellulose composite broadband terahertz absorber based on droplet jetting.

2. The method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection according to claim 1, characterized in that: During lamination and bonding, the graphene metamaterial in the nanocellulose film printed with the graphene metamaterial is arranged away from one side of the graphene / nanocellulose composite film.

3. The method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection according to claim 1, characterized in that: When preparing the graphene / nanocellulose dispersion, the mass ratio of the graphene powder to the nanocellulose powder is 1:3 to 4:

5.

4. The method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection according to claim 1, characterized in that: The mass concentration of the nanocellulose dispersion is 0.5-1.5%.

5. The method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection according to claim 1, characterized in that: When preparing graphene ink, the mass ratio of graphene powder to nanocellulose in the nanocellulose dispersion is 6:1~7:

1.

6. The method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection according to claim 1, characterized in that: When graphene ink is printed onto the nanocellulose film using a droplet jetting method, the printing rate is set to 0.6 ~ 1 mm / s.

7. The method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection according to claim 1, characterized in that: The preset pattern includes multiple structural units arranged periodically; each structural unit consists of a square ring with two intersecting and perpendicular "I" structures nested inside it; Each "I"-shaped structure includes a vertical rod and horizontal rods arranged at both ends of the vertical rod, and the two horizontal rods are arranged relatively parallel; Two mutually intersecting and perpendicular "I" structures include two "I" structures in which vertical rods are mutually intersecting and perpendicularly arranged; The two parallel horizontal bars in each "I" structure are of equal length; In each graphene metamaterial unit, a gap is left between the ends of the two cross bars in one "I" structure and the ends of the two cross bars in another "I" structure.

8. The method for preparing a graphene / nanocellulose composite broadband terahertz absorber based on droplet injection according to claim 1, characterized in that: The metal plate is copper, aluminum or silver; The thickness of the metal plate is 10-30 μm; the thickness of the graphene / nanocellulose composite film is 10-40 μm; and the thickness of the nanocellulose film printed with the graphene metamaterial is 10-40 μm.

9. A graphene / nanocellulose composite broadband terahertz absorber based on droplet injection prepared by the method according to any one of claims 1 to 8.

10. Use of the graphene / nanocellulose composite broadband terahertz absorber based on droplet injection according to claim 9 in terahertz wave absorption.

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